I would say a Goby for sure out of the 2 you mentioned.
I have seen Lawnmower Blennies sift through sand, but mine stays on Live Rock, and I don't think they eat diatoms they eat green algae, but then again, I don't think anything will eat diatoms. You are on correct path in stirring up sand instead as a way to help. Also, brown diatom algae is usually temporary in a new tank. Nasarrius Snails stir up sand also. When you get 125 gal. going, you could also look into a Jawfish.